# CVE-2026-123204: Posta before v0.18.0 SSRF via Webhook URL

Status: published. Published: 2026-11-05. Updated: 2026-11-09.

Posta before v0.18.0 contains a server-side request forgery vulnerability that allows authenticated users with edit rights to make the backend send POST requests to internal destinations by creating webhooks with arbitrary URLs. Attackers can target loopback, private-network or cloud metadata addresses and read delivery status codes and error strings to probe internal hosts and ports.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/goposta/posta/pull/315
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/goposta/posta/commit/6bb376b55dcfdcb979040ed42c4bf57b99e4f46a

## Affected products and versions

- goposta / posta (github.com/goposta/posta): ≥ 0; < v0.18.0 (affected, custom). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 5.3 (medium); CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 4.3 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N; source: CNA: VulnCheck

- CVSS 4.0: 5.3 (medium); CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: disclosure@vulncheck.com

- CVSS 3.1: 4.3 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: 0.30% as of 2026-11-09; percentile 23.07%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-918

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/goposta/posta/issues/282 (CNA: VulnCheck; issue-tracking)

- https://github.com/goposta/posta/pull/315 (CNA: VulnCheck; patch, issue-tracking)

- https://github.com/goposta/posta/commit/6bb376b55dcfdcb979040ed42c4bf57b99e4f46a (CNA: VulnCheck; patch)

- https://github.com/goposta/posta/releases/tag/v0.18.0 (CNA: VulnCheck; release-notes)

- https://github.com/goposta/posta/blob/8c3cb6f89c8a992329fac21491c38aed70d05c73/internal/services/webhook/dispatcher.go#L321-L338 (CNA: VulnCheck; technical-description)

- https://www.vulncheck.com/advisories/posta-before-0.18.0-ssrf-via-webhook-url (CNA: VulnCheck; third-party-advisory)

- https://github.com/goposta/posta/blob/8c3cb6f89c8a992329fac21491c38aed70d05c73/internal/services/webhook/dispatcher.go#L321-L338 (disclosure@vulncheck.com)

- https://github.com/goposta/posta/commit/6bb376b55dcfdcb979040ed42c4bf57b99e4f46a (disclosure@vulncheck.com)

- https://github.com/goposta/posta/issues/282 (disclosure@vulncheck.com)

- https://github.com/goposta/posta/pull/315 (disclosure@vulncheck.com)

- https://github.com/goposta/posta/releases/tag/v0.18.0 (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/posta-before-0.18.0-ssrf-via-webhook-url (disclosure@vulncheck.com)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-123204; retrieved 2026-11-09; source updated 2026-11-09

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123204; retrieved 2026-11-06; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-123204; retrieved 2026-11-09; source updated Not reported

Revision: 2b58116d4d2315655f3fb474f33ef095aeb40f685d1f77f386546e3517132104

Canonical: https://y2.dev/cve/CVE-2026-123204

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

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